U.S. patent application US 2010/0026223 describes an apparatus and method for determining the position of the rotor in a stationary rotor of a sensor-less permanent magnet synchronous machine. The system employs a rotating magnetic field to identify a magnetic axis of the rotor without a magnetic direction and then determines magnetic direction by applying pulses along the magnet axis in two polarities. In particular, in a first period, the method applies a first electrical signal to the stator coils to create a rotating stator field having a high rotational speed with a strength insufficient to cause a movement of the rotor. Current flow through the stator during this first period is used to detect a current fluctuation caused by anisotropic saliency of the permanent magnet rotor to deduce the magnetic axis. Next, in a second period after the first period, a second electrical signal is applied to the stator coils to produce a magnetic field aligned with the magnetic axis to prevent rotor motion, and current flow through this stator during the second period is used to deduce the magnetic direction and thus the orientation of the rotor. So current pulses are generated into motor to detect rotor position at standstill condition or very low speed, and the rotor magnetic polarity can be recognized. However, it is difficult or impossible to measure position when the motor rotates, and the injected current pulses may cause acoustic noise and shaft vibrations.